1. Technical Field
The invention relates to an inkjet-recording ink composition and an image-forming process using the same, and in particular, to an inkjet-recording ink composition that polymerizes and hardens by irradiation with a visible to near-infrared visible light and an image-forming process using the same.
2. Description of the Related Art
UV inks which are cured by ultraviolet ray (UV) irradiation and which have UV light-blocking properties have been known as discoloration-resistant inks (see, e.g., Japanese Patent Application Laid-Open (JP-A) No. 2003-221528). The UV-curable ink compositions currently available (see JP-A No. 2003-342503) inherently have UV ray-blocking properties and are generally compatible with a light source capable of high-illumination exposure in the UV wavelength region. Therefore, the UV-curable ink compositions has problems that such a light source costs high and that it is necessary to remove the ozone and heat generated during exposure.
In the inkjet-recording process, ink is ejected to conduct recording. Recently, inkjet printers utilizing the inkjet-recording process have been more widely used for printing on paper, film, cloth, or the like in offices as well as in general households, as the use of computers spreads. Inks such as oil ink, aqueous ink, and solid ink are known as inkjet-recording inks. Among them, aqueous inks are preferable from the points of productivity, handling, odor, stability, and the like, and are used mainly.
Because most aqueous inks use water-soluble dyes dissolving in the molecular state, the inks have advantages in high transparency and high color density. However, the aqueous inks have the following problems: the aqueous inks are less resistant to water because the dye is soluble in water; when images are printed on a so-called plain paper with an aqueous ink, the printing quality of the resulting image often deteriorate significantly owing to bleeding; the aqueous inks are also poorer in light fastness; and when printing is conducted with an aqueous ink on a recording paper having an ink-receiving recording layer containing porous inorganic particles on its surface (hereinafter, referred to as “photographic quality paper”), the storability of the image often shortens markedly owing to the influence of oxidative gases (SOx, NOx, ozone, etc.).
To overcome the problems associated with image storage, an aqueous ink containing a pigment or a dispersible dye has been proposed (see, e.g., JP-A No. 56-157468). Such an aqueous ink has somewhat improved water resistance. However, the water resistance of the aqueous ink is still insufficient. Moreover, the aqueous ink has the problems that the ink easily causes clogging in the ink ejection nozzle because the dispersion state of the pigment or the dispersible dye in the aqueous ink is unstable during storage, and that the ink containing a pigment or a dye does not penetrate into the sheet when ejected onto a photographic quality paper, and that the pigment and the dye are separated easily from the surface when rubbed with a finger, i.e., thereby lowering the abrasion resistance of the ink.
Separately, methods of covering an oil-soluble dye with a polymer have been proposed from the point of image storability (see, e.g., JP-A No. 58-45272 and JP-A No. 62-241901). However, the inkjet-recording inks obtained by the methods give images having unsatisfactory color tone and color reproducibility. In particular, the obtained images are insufficient in image fastness upon exposure to an oxidative gas or the like as, and insufficient in abrasion resistance upon printing on a photographic quality paper. In addition, an ink superior in staining property and abrasion resistance has been proposed (see, e.g., JP-A No. 2001-123097). This ink is prepared by introducing a salt-forming group and a polyalkyleneoxide group into a polymer. Images formed with the ink are resistant to abrasion with a finger, but are not sufficiently resistant to a high-level abrasion, for example, by eraser. Methods of preventing oxidative degradation of a fluorescent dye by oxygen in the air have also been proposed (e.g., JP-A No. 2002-179968). In the methods, the fluorescent dye is covered with a resin having a lower oxygen permeability. In the methods, a fluorescent dye and a resin are simply added to a solvent so that the resin covers the fluorescent dye. However, similarly to other conventional inks, the methods fail to achieve satisfactory color tone and color reproducibility.
As described above, a technology has not been established which can form an image by using an inexpensive device that does not emit ozone or heat and which can record an image superior in light fastness, ozone resistance, and abrasion resistance through curing of an ink composition by irradiation with light from such a device.